Debridement is the process of removing non-living tissue from wounds, burns and ulcers. The non-living tissue retards healing and can lead to inflammation and infection when dead tissue becomes colonized by bacteria. Sieggreen M Y and Maklebust J. “Debridement: Choices and Challenges.” Advances in Wound Care, 10 (March/April 1997): 32-37; Bale S. “A Guide to Wound Debridement.” Journal of Wound Care 6 (April 1997): 179-182. The goal of debridement therapy is to remove the non-living tissue so that the remaining tissue can begin to heal. A variety of debridement methods are known, including sharp, mechanical, biological, autolytic and enzymatic debridement.
Sharp debridement, also known as surgical debridement, utilizes a sharp object such as a scalpel, scissors, or other instrument to cut dead tissue from a wound. Sharp debridement is fast and relatively selective, i.e., it causes limited damage to healthy or healing tissue. Depending on the location of the tissue to be removed, sharp debridement can be performed at a patient's bedside or in an operating room. Typically, sharp debridement is used to treat wounds that have a large amounts of necrotic material. Sharp debridement can be costly and painful.
Mechanical debridement involves repetitive application and removal of wound dressings. According to this method, a moistened dressing is allowed to dry overnight and adhere to the dead tissue. When the dressing is removed, the dead tissue is also removed. Mechanical debridement is time-consuming, often painful, and relatively un-selective, i.e., it can produce significant damage to healthy or healing tissue. It is typically suited to treatment of wounds that have a moderate amounts of necrotic material.
Biological debridement refers to the use of sanitary maggots under dressings to cleanse wounds. See Reames M K, et al. “The use of maggots in wound debridement.” Annals of Plastic Surgery. 21: 388, 1988; Sherman, R A, Wyle, F, Vulpe, M: Maggot Debridement Therapy for treating pressure ulcers in spinal cord injury patients. Journal of Spinal Cord Medicine, 18(2): 71-74. 1995. This somewhat archaic procedure is the subject of renewed interest in recent years given its selectivity and high efficiency.
Autolytic debridement refers to the process by which dead and non-viable tissue is removed by the patient's own wound fluid, which contains growth factors, enzymes and immune cells (e.g., phagocytes) that can promote wound healing. This method utilizes occlusive or semi-occlusive dressings which maintain wound fluid in contact with the necrotic tissue. Autolytic debridement is very selective and relatively painless, but is also very slow.
Enzymatic debridement involves the use of enzymes from outside the body to remove non-living tissue. Debridement enzymes cut (“cleave” or digest) large immobile structural molecules of the cell into smaller molecules that can dissolve and migrate away. Most debridement enzymes cleave proteins, i.e., they are proteases. Enzymatic debriding agents are typically used in conjunction with moist dressings and autolytic debridement. Enzymatic debridement is relative fast and, in many cases, leaves no scar tissue.
Uses for debridement enzymes are discussed in Hobson et al., U.S. Pat. No. 6,548,556; Hobson et al., U.S. Pat. No. 6,399,092; and Jones et al., PCT Publication No. WO 2005/018695.
The effectiveness of enzymatic debridement varies with the type of enzyme used. Enzymes lie along a spectrum of selectiveness, which ranges from nonspecific (i.e., indiscriminate) digestion of protein substrates to extremely specific enzymes that can digest only one narrow type of target protein. Enzymes also differ in their productivity; the characteristic rate of digestion by an enzyme is expressed in units of activity (per gram of product), and the activity unit values are usually defined by international or pharmacopeial convention; a USP unit is defined in the United States Pharmacopeia. Many reagents and conditions can reduce the effectiveness of cleavage by a given enzyme.
Most debridement enzymes in common use are derived from non-human sources, including animals, plants and bacteria. Most commercial debriding enzymes are derived from cows, including the following four enzymes. Fibrinolysin is a plasma enzyme which, after being activated, attacks fibroin components in blood clots and exudates. Deoxyribonuclease is a pancreatic enzyme that specifically attacks nucleoprotein components of purulent exudates. These two enzymes are combined in a product known as ELASE® that finds use mostly in Europe. Trypsin and chymotrypsin are fairly nonspecific pancreatic enzymes, but they sever (i.e., cleave) substrate protein backbones at specific amino acid residues. Enzymes from other animals include krillase, a protease derived from Antarctic krill.
Tropical fruit-bearing plants provide a second source of debridement enzymes. Bromelain is a group of enzymes from the stem of pineapple plants; it includes three cysteine proteases (i.e., they have the cysteine amino acid at their active site) and the mixture breaks down tissue in the range of pH 5.5-8.5. Papain is a nonspecific cysteine protease from papaya latex that breaks down a wide variety of substances in necrotic (i.e., dead or nonviable) tissues over a wide pH range—pH 3.0-12.0; it can degrade fibroin, collagen and elastin. Ficin is a non-specific cysteine protease of similar operating pH characteristics, and is derived from a plant latex, that of the ficus (fig) plant; ficin preferentially cleaves proteins at tyrosine and phenylalanine residues.
Bacterial cultures are yet another source of debridement enzymes. Subtilisins are mixtures of relatively nonspecific, water-soluble serine proteases (i.e., they have serine at their active site), which break down necrotic tissues optimally at pH 6.0-6.8. They are derived from Bacillus subtilis bacteria. Collagenases are enzymes that attack collagen and require the presence of certain metal ions, i.e., they are metallopeptidases; commercially they are derived from Clostridium histolyticum. Vibriolysin is another very active collagen-attacking metallopeptidase, and it is derived from Vibrio proteolyticus bacteria. Thermolysin is a bacterial debridement enzyme that acts nonspecifically with outstanding productivity even at 80° C.; it is derived from Bacillus thermoproteolyticus, and requires the presence of normal wound healing cofactors such as zinc and calcium ions.
The use of thermolysin for debridement was taught by Shi et al. in US Patent Publication Nos. 2003/019863 1 A1 and 2003/0198632 A1. Streptokinase (a fibrinogen activating protease from streptococcus) and streptodornase (streptococcal deoxyribonuclease) are additional examples of bacterial proteases with value for debridement purposes.
Proteases from other types of organisms can also be useful. For instance, proteinase K is derived from the mold Tritirachium album limber. It is a senile endopeptidase that has subtilisin-like activity, and which breaks down the structural protein keratin and other proteins under alkaline conditions (e.g., pH 8 or pH 9); it is used for instance to digest cells so that their DNA and RNA can be recovered.
Several papain-urea based commercial debridement ointments are in common use to remove dead cells as part of the wound-cleaning process, including ACCUZYME®, ETHEZYME™ and PANAFIL®. According to product literature, urea is combined with papain to provide two supplementary actions: 1) to expose by solvent action the activators of papain (sulfhydryl groups) which are always present, but not necessarily accessible, in non-viable tissue or debris of lesions; and 2) to denature the non-viable protein matter in lesions and thereby render it more susceptible to enzymatic digestion. In pharmacologic studies involving digestion of beef powder, it has been shown that the combination of papain and urea produced nearly twice as much digestion as papain alone.
ACCUZYME® (HealthPoint, Fort Worth, Tex.) enzymatic debriding ointment (HealthPoint, Forth Worth, Tex.) contains papain, USP (8.3×105 USP units of activity per gram) and urea, USP 10% in a hydrophilic ointment base composed of emulsifying wax, fragrance, glycerin, isopropyl palmitate, lactose, methylparaben, potassium phosphate monobasic, propylparaben, and purified water. ACCUZYME® SE is a patent-pending delivery system that contains the same active ingredients and same units of activity as ACCUZYME®.
ETHEZYME™ (Ethex Corporation, St. Louis, Mo.) is another enzymatic debridement ointment. Each gram of ETHEZYME™ contains papain, USP (1.1×106 USP units of activity) and 100 mg urea, USP. Each gram of ETHEZYME™ 830 contains papain, USP (8.3×105 USP units of activity) and 100 mg urea, USP. Each gram of ETHEZYME™ 650 contains papain, USP (6.5 105 USP units of activity) and 100 mg urea, USP. All are in a hydrophilic ointment base composed of purified water, USP, edetate disodium, USP, emulsifying wax, NF, fragrance, glycerin, USP, isopropyl palmitate, NF, methylparaben, NF, polyoxyl 40 stearate, NF, potassium phosphate monobasic, USP, propylparaben, NF and tocopherols, mixed. All are indicated for debridement of necrotic tissue and liquefaction of pus in acute and chronic lesions such as decubitus, varicose and diabetic ulcers, burns, postoperative wounds, pilonidal cyst wounds, carbuncles and miscellaneous traumatic or infected wounds. All are applied directly to the lesion and covered with an appropriate dressing. Daily or twice daily changes are preferred.
PANAFIL® Ointment (HealthPoint, Fort Worth, Tex.) is an enzymatic healing-debriding ointment which contains standardized Papain, USP, Urea USP 10% and Chlorophyllin Copper Complex Sodium 0.5% in a hydrophilic base composed of Purified Water, USP; Propylene Glycol, USP; White Petrolatum, USP; Stearyl Alcohol, NF; Polyoxyl 40 Stearate, NF; Sorbitan Monostearate, NF; Boric Acid, NF; Chlorobutanol (Anhydrous), NF as a preservative; Sodium Borate, NF.
Some enzyme-free wound dressings have employed trace amounts of urea compounds as preservatives, thus Woller et al. in U.S. Pat. No. 5,902,600 teach the use of 0.05 to 0.50 weight percent imidurea—an oligomeric derivative of urea—as a preservative for hydrated glycerin-based wound dressings.
Normal cell and tissue is growth-limited. When growth becomes unregulated, disorders of abnormal cell proliferation result. A neoplasm is a collection of cells growing in an unregulated way. Neoplasms can be either benign or malignant (cancerous). Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). In many cancers, the cells clump together to form solid tumors, but in some the cells are dispersed around the blood stream (leukemia) or the lymphatic system (lymphoma).
The goal of cancer therapy is to selectively destroy these abnormal proliferating cells, leaving normal cells unharmed, since even a small number of remaining cancerous cells can lead to recurrence, metastasis, and death. Selectivity at the cellular level is particularly desired for the destruction of highly invasive cancers such as breast cancers in which malignant cells have become closely associated and convoluted with bone mass or other anatomical structures, thereby frustrating attempts at complete removal by surgical means. Selectivity need not be absolute, i.e., in many cases some destruction of normal cells by a therapeutic method would be tolerable if the method removed cancer cells extensively and preferentially.
Ideally, after removal of cancerous tissues, the affected site would be replenished with healthy tissue. However, removal of tumors by common therapeutic methods often results in the formation of scar tissue. This scar tissue acts as a barrier to re-entry by normal tissue, with consequent morphological disfigurement of the affected tissues even after an effective cancer treatment. Thus the use of non-scarring therapies is desired.
US Patent Publication No. 2003/0026794 A1 (Fein) discloses a method of treating skin conditions by providing compositions containing enzymes to selectively remove specific layers of skin. The depth of skin removed (that is, vertical surface treated) is regulated by the type and concentration of enzyme or enzymes in the composition. The surface area of skin removed is regulated by the area of topical application. Conditions treatable by the method are said to include, for example, age-related conditions such as lines and wrinkles, infections, pigmentary disorders, neoplasms affecting the skin, follicular disorders such as acne, and hyperkeratotic disorders such as warts.
U.S. Pat. No. 6,811,788 (Yu) teaches a method for treating a neoplasm in a mammal, comprising in situ administration of an effective amount of a hapten and a coagulation agent(s) that causes coagulation of the neoplasm, wherein the hapten is trinitrophenol and the coagulation agents are a combination of hydrogen peroxide and ethanol, and whereby an immune response is generated against the neoplasm. Yu discloses the optional addition of papain to serve as an immune response potentiator, as well as the optional addition of proteinase K, to serve as a coagulation lysing agent.
There is an ongoing need for improved treatment methods for diseases and disorders of abnormal cell proliferation, and in particular, the need for selective therapies for neoplastic diseases, including benign and malignant neoplasms and other forms of cancer.
It is therefore an object of the present to provide compositions and methods of selective enzymatic debridement for the treatment of diseases and disorders of abnormal cell proliferation, including benign and malignant neoplasms and other forms of cancer.